Sealed electrical connector

ABSTRACT

A load break electrical connector including a plug and a bushing, the plug having an electrically conductive probe and an arc-extinguishing follower mounted on the end of the probe, the bushing having an electrically conductive tubular contact and an arc-extinguishing sleeve positioned at the end of the tubular contact, a first seal mounted on the arc follower and a second seal positioned adjacent the end of the tubular contact, the seals being positioned to respectively sealingly engage the inner surface of the arc-extinguishing sleeve and the outer surface of the arc-extinguishing follower.

United States Patent [1 Sankey et al.

[ Jan. 14, 1975 SEALED ELECTRICAL CONNECTOR [75] Inventors: Edward L.Sankey, New Berlin,

Wis; Thomas J. Holtgrieve, Warren,

Ohio

[73] Assignee: RTE Corporation, Waukesha, Wis.

[22] Filed: May 3, 1974 [21] Appl. No.: 466,881

Related U.S. Application Data [63] Continuation of Ser. No, 214,603,Jan. 3, 1972,

abandoned.

[52] U.S. Cl 339/111, 339/60 R, 339/61 R, 339/94 R [51] Int. Cl HOlr13/52 [58] Field of Search 339/111, 59 R, 60 R, 60 C, 339/61 R, 94 R, 94C [56] References Cited UNITED STATES PATENTS 2,809,360 10/1957 Cobbett339/111 3,277,424 10/1966 Nelson 339/94 R 3,376,541 4/1968 Link...339/61 R 3,474,386 10/1969 Link 339/60 R Primary Examiner-Granville Y.Custer, Jr. Assistant Examiner-DeWalden W. Jones [57] ABSTRACT A loadbreak electrical connector including a plug and a bushing, the plughaving an electrically conductive probe and an arc-extinguishingfollower mounted on the end of the probe, the bushing having anelectrically conductive tubular contact and an arcextinguishing sleevepositioned at the end of the tubular contact, a first seal mounted onthe arc follower and a second seal positioned adjacent the end of thetubular contact, the seals being positioned to respectively sealinglyengage the inner surface of the arcextinguishing sleeve and the outersurface of the arcextinguishing follower.

6 Claims, 2 Drawing Figures SEALED ELECTRICAL CONNECTOR CROSS-REFERENCETO RELATED APPLICATION This application is a continuation of U.S. Ser.No. 214,603, filed Jan. 3, 1972, entitled Sealed Electrical Connector,"now abandoned.

BACKGROUND OF THE INVENTION In a safe break or load break connector ofthe type shown in U.S. Pat. No. 3,474,386, entitled ElectricalConnector, the arc created on separation is interrupted by thecooperation of an arc-interrupting follower with a cylindrical typearc-interrupting sleeve which are provided on the ends of theelectrically conductive members. It has been found that due to theinability to obtain the desired quality of arc-interrupting material forthe follower and sleeve, a restrike arc can occur on interruption.Restrike is believed to be aided by the distillation of thearc-extinguishing material due to the heat of the arc resulting in theproduction of a pressurized gas between the follower and sleeve. Thesegases when mixed with air are combustible and if ignited by the heat ofthe arc produce a highly-ionized atmosphere between the live parts ofthe connector and the adjacent electrically conductive parts of thedistribution system.

On close in, prestrike will occur when the electrically conductivemembers are a predetermined distance apart, i.e., /z to inch for 8.3kv.; to 1 inch for 15.2 kv.; 1 to 1% inches for 21.2 kv. and so on. Onprestrike, the pressure of the gas in the bushing increases rapidly andmust be vented in order to prevent rupture of the bushing.

SUMMARY OF THE INVENTION The electrical connector of the presentinvention is provided with a first seal to confine or isolate thecombustible gases created by the heat of the arc on interruption withinthe bushing. These gases are confined within the busing until the heatfrom the arc has dropped sufficiently to prevent ignition of thecombustible mixture released from the bushing or the mechanicalseparation of the bushing and elbow is far enough to prevent restrike.To minimize prestrike a second seal is positioned to engage the arcfollower either over its full length or is positioned in close proximityto the electrically conductive sleeve to increase the dielectricbreakdown strength of the creep path and thus decrease the length of theprestrike arc. Normally on close in the conductive members see to 1cycle of current during the time it takes to move the conductive membersthrough the prestrike distance.

DRA WINGS FIG. 1 is a side view, partly in section, of the electricalconnector of this invention showing the location of the seals when theconnector is disconnected. FIG. 2 is a side view, in section, of aportion of an electrical conncctor, showing alternate embodiments of theseals.

DESCRIPTION OF THE INVENTION An electrical connector of the typecontemplated herein is shown in FIG. 1 and generally includes a plug anda bushing 12. The plug 10 is connected to a high voltage, shielded cable14 and is normally provided with a semi-conductive coating 16 on theouter surface which is electrically connected to the semi-conductor 18of the cable 14. The bushing 12 is generally mounted on a housing for anelectrical device, and is electrically connected to the device by aconductive element 20 located within the housing. The electrical devicecan be a transformer located within the housing or any other type ofelectrical device. The bushing 12 is provided with anelectrically-conductive shield 22 that is grounded through the housingas is generally understood in the art. Electrical termination betweenthe cable 14 and the electrically conductive element 20 is achieved bypositioning the plug on the bushing and inserting an electricallyconductive member 24 into an electrically conductive contact 26 in thebushing.

More particularly, the plug 10 includes a housing 28 having a taperedopening 30 being formed from a dielectric material such as rubber. Theelectrically conductive probe or member 24 extends axially outwardlythrough the tapered opening 30 and is connected to the cable conductorof the shielded cable 14. An arc follower or rod 32 is provided on theouter end of the conductive member 24 and is formed of anarcextinguishing material such as Nylon.

The bushing 12 includes a housing 34 having an outer tapered surface 36which matingly engages the taperd opening 30 in the plug 10. The bushing12 has a central bore 38. The electrically conductive sleeve or contact26 is positioned within the bore 38 and is connected to the conductiveelement 20 through a conductive tube 40. A cylindrical arc snuffer ortube 42 is provided at the end of the bore 38 in a position to cooperatewith the arc-extinguishing probe 32 to confine the are produced oninterruption or close in to the space between probe 32 and the sleeve42.

The operation of an electrical connector of this type is fully describedin US. Pat. No. 3,474,386. In regard to the present invention it shouldbe understood that the heat of the are produced on interruptiondecomposes the arc extinguishing material into the space between theprobe 32 and the sleeve 42. The intense heat generated by high energyarcing causes decomposition of polymeric materials in close proximity tothe arc. Materials such as epoxy, acetals (Delrin), polyesters,silicones and fluorocarbons (Teflon) fall into the poly mer category.Decomposition of such polymers begins with breakdown of polymer chainsinto monomers and pendent side groups of much lower molecular weight,some of which are volatile in themselves others continue to break downuntil combustible. Silicone functions well under high energy arcingbecause a portion of its monomer converts to SiO thus not contributingpercent to a gaseous mixture. Due to the intense energy present duringhigh energy arcing many other atoms and elements are present. Hydrogenthough presentdoes not contribute to combustible condition of theevolved gas mixture (at least in quantity) nearly as much as thevolatile monomers and/or by products of their decomposition.

It has been found that these volatile gases are under pressure and areforced out of the bore 38 of the bushing into the recess 30 in the plugwhere they mix with air. When these gases combine with air, acombustible mixture is formed which if ignited will blow back along thesides of the bushing due to the configuration of the tapered opening 30in the plug. If these gases are ignited, a highly-ionized atmospherewill exist both within the bushing and along the outer surfaces of thebushing. This ionized atmosphere provides an electrically conductivepath between the live parts of the connector and the electricallyconductive ground shields l6 and 22 on the plug and bushing.

In accordance with the invention, means are provided to confine thegases created by the heat of the are on interruption within the bushing,until the arc temperature has been reduced or the distance between theconductive members has been increased sufficiently to eliminate thepossibility of ignition of the combustible mixture which forms onrelease of the gases from the bushing. Such means is in the form of anO-ring seal 46 on the probe 32 (FIG. 1) or an O-ring seal 44 in the arcsnuffer 42. Each of these seals will seal the interior of the bushingfrom the atmosphere and confine the gases within the bushing untilinterruption has been completed.

The O-ring seal 46 has an outer diameter slightly larger than the innerdiameter of the arc snuffer or sleeve 42 to sealingly engage the innersurface of the sleeve on close in or interruption. The O-ring seal 44has an inner diameter slightly smaller than the outer diameter of thefollower 32. These seals can be made from silicon rubber or othersimilar elastomeric materials such as Buna N or Neoprene rubber. All ofthese materials are known to have sufficient heat resistance not tocrack or disintegrate when exposed to the heat of an arc.

The critical point on current interruption occurs when the conductiveprobe 24 clears the end of the arc snuffer 42. If the gases which havebeen produced by the are on interruption within the .pace between thearc follower 32 and are snuffer 42 are released, they will combine withthe air to form a combustible mixture in the tapered recess in the plug.If these gases are ignited by the heat of the are, a highly ionizedatmosphere will exist around the end of the bushing. Restrike can occurnot only between the live parts 24 and 26 of the system but also betweenthe live parts and the ground shields 16 and 22 provided on the plug andbushing.

The gases are confined within the bore 38 of the bushing oninterruption, by means of the O-ring seal 46 provided in groove 47 inthe end of the arc follower 32 or by the O-ring seal 44 in the groove inthe sleeve 42. The gases in the bore 38 of the bushing will not bereleased until the probe clears the end of the sleeve 42. By this time,the distance between the probe 24 and the conductive sleeve 26 will begreat enough to eliminate any possibility of restrike.

In the embodiment of the invention shown in FIG. 2 an alternate form ofseal 50 is shown on the probe 32; The seal 50 is provided in a groove 52at the end of the probe 32 and is in the form of a sleeve having adiagonal cut 54 to allow for expansion and contraction of the sleeve 50.The sleeve 50 can be formed of Delrin, Nylon or Teflon.

On close in, the prestrike distance is reduced by means of the seal 48(FIG. 1) or the seal 60 (FIG. 2). The seal 48 is provided within thebore 38 of the bushing 12 in close proximity to the end of theconductive contact 26. The seal 48 can be made of the same material asthe O-ring seals 44 and 46, such as silicon rubber, Buna N or Neoprenerubber. It should be understood, however, that the sleeve seal 48 canalso be made of other dielectric materials such as Delrin, Teflon orNylon.

The seal 48 has an inner diameter slightly smaller than the outerdiameter of the arc follower 32 to provide sealing engagement with theprobe 32 as the probe is pushed into the bore 38 of the bushing 12. Onclose 5 in, the seal 48 will increase the dielectric strength ofthecreep path between the conductive members 24 and 26 thus reducing theprestrike distance minimizing the gases. These gases created from thehigh current (up to 10,000 amps.) can cause rupture of the bushing andI0 flying parts. By shortening the prestrike distance. the amount of gasis minimized because of the shorter time to which the arc extinguishingmaterials are exposed to the current.

On interruption, the seal 48 will cooperate with the IS seals 44 and 46to confine the gases in the bushing until the probe 32 clears the sleeve42. In this regard, it should be noted that the O-ring seal 46 on theprobe 32 or 50 on follower 32 will continue to confine the gases withinthe arc snuffer 42 until the probe 32 clears the end of the snuffer 42.

The seal 60 is formed on the inner surface of the sleeve 42 and is inthe form ofa coating or insert which extends the full length of thesleeve 42. The coating is molded on the inner surface of the arc snuffer42 and is made of a silicon, Buna N or Neoprene rubber. The seal 60 isretained in the sleeve 42 by means of outwardly extending flanges 62which are embedded in the sleeve 42. It should be noted that the seal 60provides protection from both restrike on interruption and prestrike onclose in.

The bushing 12 is sealed on the inner end by means of a diaphragm 60 toprevent contamination of the bushing by air in the transformer housing.This oil can enter the housing through the flexible valve sleeve 62 35and ports 64. The diaphragm should have sufficient strength to resistnormal interruption and close in pressure and to break when subjected toexplosive pressure.

RESUME An electrical connector having a seal arrangement as shown inthis invention, provides good interruption of load current withoutsubsequent restrike between the inner contacts or to the exterior groundshields. Seals are also arranged to minimize the creation of gases onclose in by reducing the prestrike distance. The seals on the arcfollower and are snuffer also cooperate to confine gases within thebushing on interruption.

We claim:

1. A high voltage load break plug for a bushing having an electricallyconductive contact and an arc extinguishing sleeve on the end of thecontact, said plug having an electrically conductive probe and anarcextinguishing follower on the end of the probe, the improvementcomprising,

a resilient seal ring mounted on the follower and having an outerdiameter equal to or greater than the inner diameter of the sleeve tosealingly engage the sleeve, said seal ring being located at the end ofthe follower remote from the probe so that the products of decompositionproduced upon interruption are confined in the space between thefollower and the sleeve and within the bushing. 2. The plug according toclaim 1 wherein said seal 65 ring comprises a first O-ring seal on theend of the follower.

3. A high voltage load break bushing for a plug having an electricallyconductive probe and an arcwithin the bushing.

4. The bushing according to claim 3 wherein said seal ring comprises anelastomeric cylindrical sleeve on the inner surface of said sleeve.

5. The bushing according to claim 3 wherein said seal ring comprises anelastomeric material covering the inner surface of said sleeve.

6. The bushing according to claim 3 wherein said seal ring comprises anO-ring.

1. A high voltage load break plug for a bushing having an electricallyconductive contact and an arc extinguishing sleeve on the end of thecontact, said plug having an electrically conductive probe and anarc-extinguishing follower on the end of the probe, the improvementcomprising, a resilient seal ring mounted on the follower and having anouter diameter equal to or greater than the inner diameter of the sleeveto sealingly engage the sleeve, said seal ring being located at the endof the follower remote from the probe so that the products ofdecomposition produced upon interruption are confined in the spacebetween the follower and the sleeve and within the bushing.
 2. The plugaccording to claim 1 wherein said seal ring comprises a first O-ringseal on the end of the follower.
 3. A high voltage load break bushingfor a plug having an electrically conductive probe and anarc-extinguishing follower on the end of the probe, the bushing havingan electrically conductive contact and an arc-extinguishing sleeve onthe end of the contact, the improvement comprising, a resilient sealring mounted within and adjacent to the open end of said sleeve tosealingly engage said follower upon interruption and having an innerdiameter equal to or smaller than the outer diameter of the follower toconfine the gases produced by the heat of the arc upon interrupton inthe space within the bushing.
 4. The bushing according to claim 3wherein said seal ring comprises an elastomeric cylindrical sleeve onthe inner surface of said sleeve.
 5. The bushing according to claim 3wherein said seal ring comprises an elastomeric material covering theinner surface of said sleeve.
 6. The bushing according to claim 3wherein said seal ring comprises an O-ring.